/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.graph.gsa;

import org.apache.flink.api.common.aggregators.Aggregator;
import org.apache.flink.api.common.functions.IterationRuntimeContext;
import org.apache.flink.types.Value;

import java.io.Serializable;
import java.util.Collection;

/**
 * The base class for the second step of a {@link GatherSumApplyIteration}.
 *
 * @param <VV> the vertex value type
 * @param <EV> the edge value type
 * @param <M> the output type
 */
@SuppressWarnings("serial")
public abstract class SumFunction<VV, EV, M> implements Serializable {

    // --------------------------------------------------------------------------------------------
    //  Attribute that allows access to the total number of vertices inside an iteration.
    // --------------------------------------------------------------------------------------------

    private long numberOfVertices = -1L;

    /**
     * Retrieves the number of vertices in the graph.
     *
     * @return the number of vertices if the {@link
     *     org.apache.flink.graph.IterationConfiguration#setOptNumVertices(boolean)} option has been
     *     set; -1 otherwise.
     */
    public long getNumberOfVertices() {
        return numberOfVertices;
    }

    void setNumberOfVertices(long numberOfVertices) {
        this.numberOfVertices = numberOfVertices;
    }

    // ---------------------------------------------------------------------------------------------
    /**
     * This method is invoked once per superstep, after the {@link GatherFunction} in a {@link
     * GatherSumApplyIteration}. It combines the partial values produced by {@link
     * GatherFunction#gather(Neighbor)} in pairs, until a single value has been computed.
     *
     * @param arg0 the first partial value.
     * @param arg1 the second partial value.
     * @return the combined value.
     */
    public abstract M sum(M arg0, M arg1);

    /**
     * This method is executed once per superstep before the vertex update function is invoked for
     * each vertex.
     */
    public void preSuperstep() {}

    /**
     * This method is executed once per superstep after the vertex update function has been invoked
     * for each vertex.
     */
    public void postSuperstep() {}

    /**
     * Gets the number of the superstep, starting at <tt>1</tt>.
     *
     * @return The number of the current superstep.
     */
    public int getSuperstepNumber() {
        return this.runtimeContext.getSuperstepNumber();
    }

    /**
     * Gets the iteration aggregator registered under the given name. The iteration aggregator
     * combines all aggregates globally once per superstep and makes them available in the next
     * superstep.
     *
     * @param name The name of the aggregator.
     * @return The aggregator registered under this name, or null, if no aggregator was registered.
     */
    public <T extends Aggregator<?>> T getIterationAggregator(String name) {
        return this.runtimeContext.getIterationAggregator(name);
    }

    /**
     * Get the aggregated value that an aggregator computed in the previous iteration.
     *
     * @param name The name of the aggregator.
     * @return The aggregated value of the previous iteration.
     */
    public <T extends Value> T getPreviousIterationAggregate(String name) {
        return this.runtimeContext.getPreviousIterationAggregate(name);
    }

    /**
     * Gets the broadcast data set registered under the given name. Broadcast data sets are
     * available on all parallel instances of a function.
     *
     * @param name The name under which the broadcast set is registered.
     * @return The broadcast data set.
     */
    public <T> Collection<T> getBroadcastSet(String name) {
        return this.runtimeContext.getBroadcastVariable(name);
    }

    // --------------------------------------------------------------------------------------------
    //  Internal methods
    // --------------------------------------------------------------------------------------------

    private IterationRuntimeContext runtimeContext;

    public void init(IterationRuntimeContext iterationRuntimeContext) {
        this.runtimeContext = iterationRuntimeContext;
    }
}
